Many types of machines that include an engine also have a radiator to supply a coolant, such as water, anti-freeze, or the like, to the engine to ensure that the engine does not overheat. The radiator is generally associated with a fan that supplies cooling air over the components of the engine, including the radiator. The radiator is typically positioned near the fan such that the fan directs air past the radiator to help cool the liquid coolant being conveyed within the radiator.
The cooling fan and engine may be housed in a shared engine compartment that includes openings to define an airflow passage through the compartment. Typically, these openings are covered with some screening material, grill, or other structure for preventing debris from entering the engine compartment. In some machines, such as tractors, off-highway trucks, compactor machines, etc., some of the blocked material can collect on these screens during machine operation, resulting in a decrease in the fan's cooling efficiency. One known strategy to address the accumulation of debris on the screen is to periodically reverse the rotational direction of the cooling fan to direct air in reverse toward the screening to dislodge any debris that may have collected on the screen surface.
In some machines, an electro-hydraulic circuit can be used to selectively switch the mode of operation of the cooling fan between forward and reverse flows. For example, U.S. Pat. No. 7,937,938 is entitled, “Hydraulic Reversing Fan Valve and Machine Using Same,” and is directed to a machine that includes a hydraulic fan system for circulating cooling air through an engine compartment. When a fan reversal event is initiated, the fan motor will continue to rotate due to angular momentum even after the pump output flow has been switched from a first motor port to a second motor port. During this continued rotation as the fan decelerates to zero speed, vacuum pressure levels can arise at the first motor port, and a pressure spike can develop at the second motor port. In order to alleviate these conditions, a pressure transfer valve briefly opens to facilitate fluid flow directly from the second motor port to the first motor port as the fan motor decelerates towards zero speed before reversing direction, simultaneously alleviating vacuum and pressure spike conditions.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some respects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.